RESUMEN
PURPOSE: To investigate the polymerization shrinkage stress of different low viscous bulk composites (SDR, Venus Bulk Fill, X-tra Base, Filtek Bulk Fill) in comparison to a conventional flowable composite (Filtek Supreme XTE Flow) and to high viscous bulk and conventional composites (Filtek Supreme XTE, GrandioSO, Tetric EvoCeram, Tetric EvoCeram BulkFill, Venus Diamond, Venus Pearl), as well as to an experimental composite (Ormocer) and a sonic-activated bulk fill composite (Sonicfill), by means of photoelastic investigation. METHODS: To ensure bonding of the resin composite, cylindrical cavities (Ø 4mm) in araldite B epoxide resin plates (40 × 40 × 4 mm3) were pre-treated with the Rocatec system. Embedded in araldite plates, six resin composite specimens of each material were exposed for 60 seconds from one side (Translux Power Blue, 1,000 mW/cm2). The samples were stored, light-protected and dry (23°C). Polymerization shrinkage stress data (MPa) were calculated 15 minutes, 1 and 24 hours after light exposure, based on the diameter of the isochromatic curves of first order, obtained from araldite plates. Statistical analysis was performed with the Wilcoxon-test and Bonferroni correction (P< 0.0006). RESULTS: After 15 minutes/1 hour, the mean polymerization stress values calculated were:for SDR 4.4 ± 0.1/4.4 ± 0.2 MPa; Venus Bulk Fill 4.8 ± 0.3/4.9 ± 0.3 MPa; X-tra Base 6.5 ± 0.3/6.7 ± 0.3 MPa; Filtek Bulk Fill 4.9 ± 0.3/4.9 ± 0.3 MPa; Filtek Supreme XTE Flow 8.0 ± 0.3/8.2 ± 0.2 MPa; Filtek Supreme XTE 7.1 ± 0.1/7.4 ± 0.2 MPa; GrandioSO 6.3 ± 0.4/6.3 ± 0.3 MPa; Tetric EvoCeram 4.5 ± 0.1/4.6 ± 0.1 MPa; Tetric EvoCeram BulkFill 4.9 ± 0.2/5.0 ± 0.3 MPa; Venus Diamond 3.7 ± 0.3/3.8 ± 0.3 MPa; Venus Pearl 3.9 ± 0.2/4.0 ± 0.2 MPa, Sonicfill 5.4 ± 0.2/5.6 ± 0.3 MPa; and Ormocer (experimental) 4.1 ± 0.2/4.3 ± 0.2 MPa. After 24 hours, the following mean stress values were obtained:SDR 4.7 ± 0.2 MPa; Venus Bulk Fill 5.1 ± 0.2 MPa; X-tra Base 7.2 ± 0.4 MPa; Filtek Bulk Fill 5.3 ± 0.3 MPa; Filtek Supreme XTE Flow 8.7 ± 0.3 MPa; Filtek Supreme XTE 7.9 ± 0.2 MPa; GrandioSO 7.0 ± 0.4 MPa; Tetric EvoCeram 4.9 ± 0.1 MPa; Tetric EvoCeram BulkFill 5.4 ± 0.3 MPa; Venus Diamond 4.5 ± 0.3 MPa; Venus Pearl 4.5 ± 0.3 MPa, Sonicfill 5.8 ± 0.2 MPa and Ormocer (experimental) 4.5 ± 0.2 MPa. The new and experimental resin composites showed significantly less polymerization shrinkage stress than the conventional resin composite (Filtek Supreme XTE). CLINICAL SIGNIFICANCE: Resin composite restoratives differ in their polymerization shrinkage stress development, independent of their viscosity. Some low viscosity bulkfill-restoratives generate less shrinkage stress compared to other conventional or bulk-restoratives. Practitioners should yield to the potential effect of shrinkage stress development, because this might affect marginal integrity in the clinical performance.